Research description

Current projects

Biochemical and genetic regulation of the metabolic processes that are required for symbiotic nitrogen fixation is the focus of this research program. Rhizobium-leguminous plant symbioses are unique associations in which both the bacteria and the plant undergo complex metabolic and morphological changes. My laboratory is attempting to identify these processes and to elucidate the mechanisms by which these changes are controlled. The primary goal is to determine which factors, genetic and/or biochemical, limit nitrogen fixation and thus plant growth and development. After these limitations are defined, the appropriate generic alterations will then be attempted to enhance plant productivity.

Specific projects include:

Genomic analysis using oligonucleotide microarrays of the Bradyrhizobium japonicum genome

Proteomic analysis of the proteins expressed during symbiotic development; and

A recent focus of the laboratory has been the elucidation of malate metabolism by the symbiotic form of B. japonicum which are referred to as bacteroids and the role of alanine excretion by bacteroids. Malate is the primary compound provided to the bacterorid by the plant and is believed to be metabolized via the citric acid cycle, but we have shown that neither α-ketoglutarate dehydrogenase nor isocitrate dehydrogenase are required for symbiotic nitrogen fixation. Thus, the pathway of malate metabolism to provide energy for reduction of atmospheric dinitrogen remains to be determined. Recently, we have shown that alanine, not ammonium, is the principle nitrogen compound provided to the plant by the bacteroid. The metabolism of B. japonicum is being characterized via DNA microarray and proteomic analysis.